Plasma imipramine and desmethylimipramine levels are assayed by gas chromatography. Blood samples from depressed patients treated with imipramine are collected at five collaborating centers. To determine whether a therapeutic range for plasma imipramine and/or desmethylimipramine exists for unipolar and/or bipolar recurrent affective illiness in the acute phase and in patients requiring long-term maintenance therapy with tricyclic antidepressants. To evaluate the relationship between toxic side effets and plasma levels of imipramine and desmethylimipramine during long-term maintenance therapy. To determine whether lithium affects plasma levels of imipramine and desmethylimipramine. The analytical method to be used involves gas liquid chromatography using a nitrogen detector.